Testing the Efficacy of Biosolids to Promote Ecological Restoration on Mine Spoils

Re-establishing native plant communities is critical for restoring post-mine influenced sites. A major challenge is that mining activity can result in poor soil quality that is not conducive to plant growth. Various soil amendments can provide organic material and nutrients that assist plant growth. Biosolids, treated solids recovered from municipal wastewater, can be used as a soil amendment to improve soil quality of mine-influenced landscapes and provide the nutrients for plant growth. The objectives of this study were (1) to determine an appropriate rate of biosolid application to promote the colonization of native plants and (2) to determine the effects of the biosolids on soil properties. In 2021, a field study was devised that tested four biosolid application rates (0, 125, 250, and 375 dry Mg/ha). The site was located in a mining area in the southern interior of British Columbia, Canada, with six replicates per experimental combination. This study demonstrated that biosolids significantly increased the productivity and diversity of the plant community. Biosolids reduced soil pH and increased soil organic matter, carbon and nitrogen concentrations. Receiving soils were either similar to or marginally high in arsenic (As) and molybdenum (Mo). In contrast, biosolids tended to significantly increase Cu levels compared to the control soils. Higher rates of biosolids did not lead to significantly higher plant productivity or diversity than the lower rates. The results of this study suggest that biosolids may significantly help restore sustainable grassland ecosystems in post-mining environments even at a lower application rate of 125 dry Mg/ha.